1. Field of the Invention
This invention relates to an AD converter evaluation apparatus and in particular to a high-resolution AD converter evaluation apparatus for automatically measuring an AD converter to be measured using a computer, etc.
2. Description of the Related Art
FIG. 4 shows an AD converter evaluation apparatus in a related art. The AD converter evaluation apparatus will be discussed.
An AD converter evaluation apparatus 40 in the related art automatically measures an AD converter 50 to be measured using a computer 43, etc. The AD converter evaluation apparatus 40 has a programmable power supply 41, a controller 42 connected to the computer 43 by a PCI bus 45, a buffer amplifier 49, and the AD converter 50, as shown in FIG. 4.
The controller 42 has a GPIB interface 47 connected to the programmable power supply 41 by a GPIB cable 44 and an I/O interface 46 connected to the AD converter 50 by an AD converter conversion start signal line 48.
Thus, output of the programmable power supply 41 is connected to the buffer amplifier 49, an output signal of the buffer amplifier 49 is input to the AD converter 50, and an AD converter conversion start signal is transmitted from the controller 42 for controlling and evaluating the AD converter 50.
To evaluate the AD converter, the precision of the signal source need be higher precision about four bits than the number of output bits of the AD converter to be measured.
Thus, it is very difficult to provide a programmable power supply to evaluate an AD converter having a resolution of 12 bits or more.
For example, to measure an AD converter with output 0 to 5 V having a resolution of 16 bits, it becomes necessary to set a voltage finer than 4.75 xcexcV.
It is therefore an object of the invention to provide an AD converter evaluation apparatus that can produce programmable power supply having a high resolution required for measuring an AD converter to be measured.
According to the present invention, there is provided an AD converter evaluation apparatus for evaluating an AD converter, including:
a first programmable power supply for applying a first voltage;
a second programmable power supply for applying a second voltage;
an attenuator circuit for attenuating the second voltage output from the second programmable power supply to generate a third voltage;
an addition circuit for adding the third voltage of the attenuator circuit to the first voltage output from the first programmable power supply to generate a fourth voltage; and
a digital multimeter for measuring the first voltage of the first programmable power supply and the second voltage of the second programmable power supply,
wherein the fourth voltage of the addition circuit is input to the AD converter.
Accordingly, the output of one programmable power supply is attenuated by the attenuator circuit and the result and the output of the other programmable power supply are added together, whereby higher-resolution programmable power supply can be realized and the object can be accomplished.
The AD converter evaluation apparatus further includes:
a computer; and
a controller connected to the computer and connected through an interface section to the digital multimeter and the AD converter, the controller for controlling the AD converter.
Accordingly, the AD converter evaluation apparatus can be automatically controlled by the computer.
In the AD converter evaluation apparatus, the digital multimeter measures the fourth voltage of the addition circuit and outputs an actual measured voltage of the fourth voltage to the computer. The computer compares the actual measured voltage with an expected voltage of the fourth voltage programmed in the computer in advance to calculate a difference between the actual measured voltage and the expected voltage. The computer resets the first and second voltages of the first and second programmable power supplies, thereby to cancel out an error component thereof. The reset first and second voltages of the first and second programmable power supplies are input to the AD converter. The controller transmits an AD converter conversion start signal to start conversion operation of the AD converter.
Accordingly, the actual measurement value input to the digital multimeter is compared with the expected value programmed in the computer in advance, the difference between the actual measurement value and the expected value is found, and the values of the programmable power supplies are again set, whereby the measurement error can be canceled out and output voltage close to the precision of the digital multimeter can be provided.